Apparatus for fabricating a III-V nitride film

ABSTRACT

An apparatus for fabricating a III-V nitride film by a MOCVD method, including a reactor prepared horizontally, a susceptor to hold a substrate thereon installed in the reactor, a heater to heat the substrate to a predetermined temperature via the susceptor, and a cooling mechanism to directly cool down at least the portion of the inner wall of the reactor opposite to the substrate.

BACKGROUND OF THE INVENTION

[0001] (1) Field of the Invention

[0002] This invention relates to a method to epitaxially grow a III-Vnitride film, particularly AlxGayInzN (x+y+z=1) film on a givensubstrate by a Metal Organic Chemical Vapor Deposition (MOCVD) methodand an apparatus for the same method.

[0003] (2) Related Art Statement

[0004] In opto-electronic devices such as light-emitting diodes, laserdiodes or photodiodes, it is proposed that III-V nitride films havingtheir compositions of AlxGayInzN(X+Y+Z=1) is epitaxially grown on agiven substrate made of sapphire single crystal, for example. Up to now,the epitaxial growth of the AlxGayInzN film has been performed by aMOCVD method or recently, a Hydride Vapor Phase Epitaxy (HVPE) method.

[0005] In the case of making a GaN film by a HVPE method, first of all,a substrate made of sapphire single crystal is set into a reactor inwhich a gallium metallic material is charged. Then, a hydrochloric acidgas is introduced into the reactor and reacted with the gallium metallicmaterial, to generate a hydrochloric gallium gas. Then, an ammonia gasis introduced into the reactor and reacted with the hydrochloric galliumgas, to deposit and fabricate the GaN film on the substrate. The HVPEmethod has a higher film growth rate than a MOCVD method or a MOVPEmethod. For example, in the MOVPE method, a GaN film can be epitaxiallygrown typically at only several μm/hour, but in the HVPE method, the GaNfilm can be epitaxially grown typically at several hundreds μm/hour.Therefore, the HVPE method has its advantage in forming a thicker III-Vnitride film.

[0006] However, a good quality AlxGayInzN film can not be provided bythe HVPE method, and the fluctuation in thickness on the same substratemay be increased. On the other hand, it takes much time to form theAlxGayInzN film by the MOVPE method, and thus, the fabrication cost ofthe AlxGayInzN film is risen.

[0007] In the case of making an AlxGayInzN (x+y+z=1) film by a MOCVDmethod, a given substrate is set and held on a susceptor installed in areactor, and is heated to a predetermined temperature by a heater. Then,a trimethylaluminum gas, a trimethylgallium gas, a trimethylindium gasor the like as III raw material gases are introduced with a carrier gascomposed of a hydrogen gas or a nitrogen gas into the reactor. Anammonia gas as a V raw material gas is introduced with a carrier gascomposed of a hydrogen gas or a nitrogen gas into the reactor. Then, theIII raw material gases and the V raw material gas are reacted, todeposit and form the AlxGayInzN film on the substrate. As the AlxGayInzNfilm, an aluminum nitride film, a gallium nitride film, an indiumnitride film, an aluminum-gallium nitride film, an aluminum-indiumnitride film and a gallium-indium nitride film are exemplified.

[0008] In the above conventional method such as a MOCVD method, if thereaction between the III raw material gases and the V raw material gasis created on the wall surfaces of the reactor, the film-formingefficiency is degraded, and thus, the film growth rate is decreased. Inthe past, therefore, although it is considered that a cooling jacket isattached to the reactor, it is very difficult to directly attach thecooling jacket to the reactor because the reactor is made of quartz intoa complicated figuration. As a result, the reactor is covered with astainless tube on which a cooling jacket is attached.

[0009] In such a conventional fabricating apparatus, since the reactoris only indirectly cooled by the cooling jacket, it can not be cooleddown sufficiently. Particularly, it was confirmed that an AlN film or anAl-rich AlxGayInzN (x+y+z=1, x>0.5, y≧0, Z≧0) film can not be fabricatedsufficiently, as compared with a GaN film or an Al-poor AlxGayInzN(x+y+z=1, 0≦x<0.5, y≧0, Z≧0) film. The reason is because in fabricatingsuch an Al-rich AlxGayInzN film, a large amount of trimethyl-aluminumand a large amount of ammonia are employed as raw material gases andthus, the large proportions of the raw material gases are reacted on thewall of the reactor and on the susceptor heated to a higher temperature.As a result, the epitaxial growth of the Al-rich AlxGayInzN (x+y+z=1,x>0.5, y≧0, Z≧0) film is inhibited.

[0010] Particularly, in the case that the susceptor is set on the bottomwall of the reactor and the substrate is set on the susceptor so thatthe main surface of the substrate is faced to the top wall of thereactor, a large amount of aluminum nitrides may be deposited on the topwall because the top wall is easy to be heated to a high temperature dueto the radiant heat from the susceptor. Since the aluminum nitrides maybe broken away from on the top wall and introduced into the growingAl-rich AlxGayInzN film, the crystal quality of the Al-rich AlxGayInzNfilm may be deteriorated.

[0011] In light of the above-mentioned problems, such a technique as tocool down the raw material gases with the cooling jackets attached tothe nozzles to introduce the raw material gases into the reactor isdisclosed in the Japanese Laid-open Publications Kokai Hei 10-167883(JPA 10-167883) and Kokai Hei 10-67884 (JPA 10-67884). Moreover, such atechnique as to cool down the raw material gases around the susceptorwith a cooling jacket provided on the upper side from the susceptor isdisclosed in the Japanese Laid-open Publication Kokai Hei 10-100726 (JPA 10-100726).

[0012] According to such a conventional technique, although the filmgrowth rate and the crystal quality of the Al-rich AlxGayInzN film canbe improved to some degree, they are not sufficient. Particularly, sincethe portion of the top wall of the reactor opposing to the substrate onthe susceptor is not cooled down sufficiently, the broken away aluminumnitrides may deteriorate the crystal quality of the Al-rich AlxGayInzNfilm to large degree.

[0013] In addition, when using the conventional technique, thefluctuation in thickness of the AlxGayInzN film is increased.Particularly, when employing a larger substrate such as a 3-inch wafer,the fluctuation in thickness becomes conspicuous.

[0014] Moreover, it is proposed that a vertical reactor tube is employedand a substrate is set vertically in the reactor tube, that is,substantially parallel to the wall of the reactor tube. In this case,although raw material gases are introduced into the reactor tube fromthe top via nozzles cooled down with a cooling jacket, the nozzles maybe stopped up through the reaction between the raw material gases in thenozzles.

SUMMARY OF THE INVENTION

[0015] It is an object of the present invention to work out the aboveconventional problems, and thus, to provide a method for epitaxiallygrowing a good quality AlxGayInzN (x+y+z=1, x≧0, y≧0, Z≧0) film at ahigher film growth rate without the fluctuation in thickness by a MOCVDmethod.

[0016] It is another object of the present invention to provide anapparatus for epitaxially growing a good quality AlxGayInzN (x+y+z=1,x≧0, y≧0, Z≧0) film at a higher film growth rate without the fluctuationin thickness by a MOCVD method.

[0017] In order to achieve the above object, this invention relates to amethod for fabricating a III-V nitride film, including the steps ofpreparing a reactor horizontally, setting a substrate onto a susceptorinstalled in the reactor, heating the substrate to a predeterminedtemperature, directly cooling at least the portion of the inner wall ofthe reactor opposite to the substrate, and introducing a III rawmaterial gas and a V raw material gas with a carrier gas onto thesubstrate, and thus, fabricating a III-V nitride film by a MOCVD method.

[0018] The effect of the present invention can be exhibited in the casethat in forming the III-V nitride film, the susceptor is set on thebottom wall of the reactor so as to oppose the top wall of the reactor,and the substrate is set on the susceptor so that the main surface ofthe substrate is opposed to the top wall of the reactor. However; thesusceptor may be set on the top wall of the reactor, and the substrateis set on the susceptor so that the main surface of the substrate isopposed to the bottom wall of the reactor.

[0019] According to the present invention, a large amount oftrimethylaluminum and a large amount of ammonia are introduced into thereactor as raw material gases, to be able to fabricate an Al-richAlGaInN (x+y+z=1, x>0.5, y≧0, Z≧0) film or an AlN film in good qualityat a higher film growth rate by a MOCVD method.

[0020] In the present invention, the substrate may be made of oxidesingle crystal such as sapphire single crystal, ZnO single crystal,LiAlO₂ single crystal, LiGaO₂ single crystal, MgAl₂O₄ single crystal, orMgO single crystal, IV single crystal or IV-IV singe crystal such as Sisingle crystal or SiC single crystal, III-V single crystal such as GaAssingle crystal, AlN single crystal, GaN single crystal or AlGaN singlecrystal, and boride single crystal such as ZrB₂. Moreover, the substratemay be made of an epitaxial substrate composed of a base material madeof the above-mentioned single crystal and an epitaxial film made ofoxide single crystal such as ZnO single crystal or MgO single crystal,IV single crystal or IV-IV single crystal such as Si single crystal orSiC single crystal, III-V single crystal such as GaAs single crystal,InP single crystal, AlN single crystal, GaN single crystal or AlGaNsingle crystal, and boride single crystal such as ZrB₂.

[0021] This invention also relates to an apparatus for fabricating aIII-V nitride film by a MOCVD method, including a reactor preparedhorizontally, a susceptor to hold a substrate thereon installed in thereactor, a heater to heat the substrate to a predetermined temperaturevia the susceptor, and a cooling means to directly cool down at leastthe portion of the inner wall of the reactor opposite to the substrate.

[0022] In a preferred embodiment of the fabricating apparatus of thepresent invention, the portions of the inner wall of the reactoropposite to the susceptor and in the upper stream from the substrate ofthe raw material gases are cooled down with the cooling means. In thiscase, two cooling jackets may be prepared for the portions opposite tothe susceptor and in the upper stream from the substrate. The coolingjacket may be made of stainless steel. As a result, the configuration ofthe apparatus is simplified, and thus, the cost of the apparatus can belowered

[0023] In another preferred embodiment of the fabricating apparatus ofthe present invention, the cooling means includes a cooling jacketdirectly attached to or built in the inner wall of the reactor, a pumpto circulate a cooling medium through the cooling jacket and a coolingmedium temperature-controlling instrument. As the cooling medium, watermay be exemplified.

[0024] In still another preferred embodiment of the fabricatingapparatus of the present invention, the reactor with the cooling meansis covered with a housing entirely, and another cooling means isprovided on the outer side of the housing. In this case, the whole ofthe reactor can be cooled down effectively.

[0025] In a further preferred embodiment of the fabricating apparatus ofthe present invention, the reactor is made of stainless steel entirely,and the whole of the reactor is cooled down directly with the coolingmeans. In this case, the configuration of the reactor can be simplified,and thus, the fabricating cost of a III-V nitride film can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] For better understanding of the present invention, reference ismade to the attached drawings, wherein

[0027]FIG. 1 is a cross sectional view schematically showing a firstembodiment of the fabricating apparatus of the present invention,

[0028]FIG. 2 is a cross sectional view schematically showing a secondembodiment of the fabricating apparatus of the present invention,

[0029]FIG. 3 is a cross sectional view schematically showing a thirdembodiment of the fabricating apparatus of the present invention,

[0030]FIG. 4 is a cross sectional view schematically showing a fourthembodiment of the fabricating apparatus of the present invention,

[0031]FIG. 5 is a graph showing a film growth rate of a III-V nitridefilm in using a fabricating apparatus according to the presentinvention, in comparison with the one using a conventional fabricatingapparatus, and

[0032]FIG. 6 is a graph showing a distribution in thickness of a III-Vnitride film on a 3-inch wafer in using a fabricating apparatusaccording to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033]FIG. 1 is a cross sectional view schematically showing a firstembodiment of the fabricating apparatus of the present invention. Inthis embodiment, an AlN film is formed on a sapphire single crystalsubstrate. The fabricating apparatus depicted in FIG. 1 includes areactor 11 set horizontally and made of quartz entirely, and a susceptor13 located at the almost center of the bottom wall of the reactor 11.Then, a heater 14 is provided under the susceptor 13. A sapphire singlecrystal substrate 12 is set and held on the susceptor 13 upwardly, andheated with the heater 14 to a given temperature via the susceptor 13.By disposing the susceptor 13 at the top wall of the reactor 11, thesubstrate 12 is set and held on the susceptor downwardly.

[0034] At the right side of the reactor 11 are provided gas inlets 15-17to introduce raw material gases with a carrier gas. In the case ofmaking an AlN film, a trimethylaluminum gas is introduced with ahydrogen carrier gas from the first gas inlet 15, and an ammonia gas isintroduced from the second gas inlet 16. Then, a carrier gas composed ofa hydrogen gas and a nitrogen gas is introduced from the third gas inlet17. The introduced trimethylaluminum gas and the introduced ammonia gasare also introduced into the center region of the reactor throughseparated guiding tubes 18 and 19, respectively. In this case, the rawmaterial gases are effectively supplied onto the substrate 12, and notsupplied in the remote region from the substrate 12. Therefore, theintroduced raw material gases are consumed by a MOCVD reaction on thesubstrate.

[0035] Then, a cooling jacket 20 made of stainless steel is provided atthe outer side of the top wall of the reactor opposite to the substrate12. A first cooling medium temperature-controlling instrument 21 and apump 22 are connected to the cooling jacket 20, and thus, a givencooling medium is flown through the cooling jacket 20 with the pump 22.The temperature of the cooling medium is controlled with the controllinginstrument 21. Moreover, at the left side of the reactor 11 is provideda ventilation duct 23, and the remaining raw material gases not consumedare exhausted from the ventilation duct 23.

[0036] The substrate 12 is heated to around 1000° C., for example by theheater 14, and the interior temperature and the inner wall temperatureof the reactor 11 to which the raw material gases are directly contactedare cooled down by flowing the cooling medium through the cooling jacket20. Particularly, the center of the top wall opposite to the substrate12 is cooled down effectively. Therefore, the reaction between the rawmaterial gases can be reduced effectively on the inner wall,particularly on the center of the inner top wall, and can be enhanced onthe substrate 12. As a result, an AlN film can be formed at a higherfilm growth rate, and the crystal quality of the AlN film can bedeveloped through the inhibition of the deposition and thus, thebreakaway of the aluminum nitride on or from the inner wall of thereactor.

[0037]FIG. 2 is a cross sectional view schematically showing a secondembodiment of the fabricating apparatus of the present invention. Thesame reference numerals are given to the similar constituent portions tothe ones depicted in FIG. 1. In this embodiment, too, the fabricatingapparatus depicted in FIG. 2 includes a reactor 11 set horizontally andmade of quartz entirely, and a susceptor 13 located at the almost centerof the bottom wall of the reactor 11. Then, a heater 14 is providedunder the susceptor 13. A sapphire single crystal substrate 12 is setand held on the susceptor 13 upwardly, and heated with the heater 14 toa given temperature via the susceptor 13. Moreover, a cooling jacket 20made of stainless steel and having a first cooling mediumtemperature-controlling instrument 21 and a pump 22 is provided at theouter side of the top wall of the reactor opposite to the substrate 12.

[0038] At the right side of the reactor 11 are provided gas inlets 15-17to introduce raw material gases with a carrier gas. A trimethylaluminumgas is introduced with a hydrogen carrier gas from the first gas inlet15, and an ammonia gas is introduced from the second gas inlet 16. Then,a carrier gas composed of a hydrogen gas and a nitrogen gas isintroduced from the third gas inlet 17. The introduced trimethylaluminumgas and the introduced ammonia gas are also introduced into the centerregion of the reactor through separated guiding tubes 18 and 19,respectively. In this case, too, the raw material cases are effectivelysupplied onto the substrate 12, and not supplied in the remote regionfrom the substrate 12. Therefore, the introduced raw material gases areconsumed by a MOCVD reaction on the substrate.

[0039] In this embodiment, for cooling the upper stream side of thereactor 11, a second cooling jacket 30 is provided at the upper streamside. To the second cooling jacket 30 are connected a second coolingmedium temperature-controlling instrument 31 and a pump 32. Then, agiven cooling medium is flown through the cooling jacket 30 with thepump 32, as well as the first cooling jacket 20. The first and thesecond cooling jackets 20 and 30 may be combined and composed of asingle cooling jacket.

[0040] In this embodiment, by flowing a given cooling medium through thefirst and the second cooling jackets 20 and 30, the interior temperatureand the inner wall temperature of the reactor 11 to which the rawmaterial gases are directly contacted are cooled down. Particularly, thecenter of the top wall opposite to the substrate 12 and the upper streamside of the reactor 11 are cooled down effectively. As a result, an AlNfilm can be formed at a much higher film growth rate, and the crystalquality of the AlN film can be more developed through the inhibition ofthe deposition and thus, the breakaway of the aluminum nitride on orfrom the inner wall of the reactor.

[0041]FIG. 3 is a cross sectional view schematically showing a thirdembodiment of the fabricating apparatus of the present invention. Thesame reference numerals are given to the similar constituent portions tothe ones depicted in FIGS. 1 and 2, and detail explanations for thesimilar constituent portions are omitted.

[0042] In this embodiment, the reactor 11 is covered with a housing 40made of quartz almost entirely. Outside of the housing 40 are provided athird cooling jacket 41 so as to cover the gas inlets 15-17, a fourthcooling jacket 42 at the center of the reactor 11 and a fifth coolingjacket 43 so as to cover the ventilation duct 23. To the cooling jackets41-43 are connected their respective cooling mediumtemperature-controlling means and pumps not shown. A given coolingmedium is flown through the cooling jackets 41-43 in the directionsdesignated by the arrows. In between the reactor 11 and the housing 40is a carrier gas composed of a hydrogen gas and a nitrogen gas from agas inlet 44.

[0043]FIG. 4 is a cross sectional view schematically showing a fourthembodiment of the fabricating apparatus of the present invention. Thesame reference numerals are given to the similar constituent portions tothe ones depicted in FIGS. 1-3. In this embodiment, a cooling jacket 51is provided on the top wall of the reactor entirely, and a secondcooling jacket 52 is provided in the bottom wall of the reactor entirelyexcept the susceptor 13 and the heater 14.

[0044] To the first cooling jacket 51 are connected a first coolingmedium temperature-controlling instrument 53 and a first pump 54, and tothe second cooling jacket 52 are connected a second cooling mediumtemperature-controlling instrument 55 and a second pump 56. Then, thegas inlets 15-17 are provided at the right side of the reactor 11, andthe ventilation duct 23 is provided at the left side of the reactor 11,as well as FIGS. 1-3.

[0045]FIG. 5 is a graph showing film growth rates of AlN filmsfabricated by using the fabricating apparatuses in the third and thefourth embodiments shown in FIGS. 3 and 4, respectively, in comparisonwith the ones fabricated by using a conventional fabricating apparatus.In this case, the same condition is employed. In the case of using theconventional apparatus, the film growth rate was only 0.5 μm/hr. On theother hand, in the case of using the apparatus of the third embodimentin which the upper stream side of the reactor is particularly cooleddown, the film-forming rate is developed to about 1 μm/hr. Moreover, inthe case of using the apparatus of the fourth embodiment in which thewhole of the reactor is almost cooled down, the film growth rate isdeveloped to about 1.2 μm. As a result, it is turned out that thefilm-forming efficiency can be enhanced according to the presentinvention.

[0046]FIG. 6 is a graph showing a distribution in thickness of an AlNfilm fabricated on a 3-inch wafer by using the apparatus of the fourthembodiment shown in FIG. 4. The zero point of the abscissa axisdesignates the center of the wafer, and thus, the abscissa itselfdesignates the distance of the center on the wafer. The vertical axisdesignates the thickness of the AlN film in order of angstrom. As isapparent from FIG. 6, the distribution in thickness on the 3-inch waferis repressed within 1.8%, and thus, it is turned out that the AlN filmcan be formed uniformly on such a larger substrate by using theapparatus of the present invention.

[0047] Although the present invention was described in detail withreference to the above example, this invention is not limited to theabove disclosure and every kind of variation and modification may bemade without departing from the scope of the present invention. Insteadof such an AlN film, an Al-rich AlxGayInzN (x+y+z=1, x>0.5, y≧0, Z≧0)film may be fabricated. Besides, an Al-poor AlxGayInzN (x+y+z=1,0≦x<0.5, y≧0, Z≧0) film may be fabricated. Moreover, instead of sapphiresingle crystal, the substrate 12 may be made of oxide single crystalsuch as ZnO single crystal, LiAlO₂ single crystal, LiGaO₂ singlecrystal, MgAl₂O₄ single crystal, or MgO single crystal, IV singlecrystal or IV-IV single crystal such as Si single crystal or SiC singlecrystal, III-V single crystal such as GaAs single crystal, AlN singlecrystal, GaN single crystal or AlGaN single crystal, and boride singlecrystal such as ZrB₂. In addition, the substrate may be made of anepitaxial substrate composed of a base material made of theabove-mentioned single crystal and an epitaxial film made of oxidesingle crystal such as ZnO single crystal or MgO single crystal, IVsingle crystal or IV-IV single crystal such as Si single crystal or SiCsingle crystal, III-V single crystal such as GaAs single crystal, InPsingle crystal, AlN single crystal, GaN single crystal or AlGaN singlecrystal, and boride single crystal such as ZrB₂.

[0048] In the above-mentioned fourth embodiment, although the coolingjackets 51 and 52 made of stainless steel are provided on the outer sideof the reactor 11, the reactor 11 itself may be partially made as acooling jacket.

[0049] As mentioned above, according to the method and the apparatus forfabricating a III-V nitride film, since the inner wall of the reactor towhich raw material gases are directly contacted is directly cooled down,the reaction between the raw material gases can be prevented on theinner wall. Therefore, the film-forming efficiency can be developed andthus, the film growth rate can be developed, particularly in fabricatingan AlN film or an Al-rich AlxGayInzN (x+y+z=1, x>0.5, y≧0, Z≧0) filmusing a large amount of trimethylaluminum and a large amount of ammonia.In addition, since the opposite portion of the inner wall of the reactorto the substrate is cooled down, the deposition and the breakaway ofaluminum nitrides on and from the inner wall can be inhibited, and thus,the crystal quality of a III-V nitride film can be developed.

[0050] Moreover, since the reactor is made of quartz and the coolingjacket is made of stainless steel, the configuration of the apparatuscan be simplified, and the cost of the apparatus can be lowered. Then,the fabricating cost of the III-V nitride film can be reduced due to theeasy maintenance.

What is claimed:
 1. An apparatus for fabricating a III-V nitride film bya MOCVD method, comprising: a reactor prepared horizontally, a susceptorto hold a substrate thereon installed in the reactor, a heater to heatthe substrate to a predetermined temperature via the susceptor, and acooling means to directly cool down at least the portion of the innerwall of the reactor opposite to the substrate.
 2. A fabricatingapparatus as defined in claim 1, wherein the cooling means includes acooling jacket, a pump to flow a given cooling medium through thecooling jacket and a cooling medium temperature-controlling means tocontrol the temperature of the cooling medium.
 3. A fabricatingapparatus as defined in claim 1, wherein the cooling jacket is made ofstainless steel and the reactor is made of quartz.
 4. A fabricatingapparatus as defined in claim 1, wherein the cooling means is providedover the reactor entirely.
 5. A fabricating apparatus as defined inclaim 1, further comprising a housing on the outer side of the reactor,wherein the cooling means is provided on the outer side of the housing.6. A fabricating apparatus as defined in claim 1, further comprisinganother cooling means at the upper stream of the reactor from thesubstrate set on the susceptor.